Manufacture of chloroprene



Patented Apr. 14, 1953 Z 2;635,12-2 .EMANUFACTU-RE OF QHLOROBRENE S'James' H. Dunn, ClarencefM. Maker; and Tony ICorporation; New York, N.'l

Delaware a.:-assignorsitoEthyl .grazcorporation of fNdDraw ing'. iiflpblicationiNovemberZ8iI950,

. "'SeriaPNo. 194,724

i3.Glaims.

- ll'iis' inventiomrelates to the'manutacturetof *isltloroprene. More "particularly, the invention relates toaprocess--whereby",chloroprene ispro duced by a *new' reaction which ':utilizes a new a "more "economical starting material than hitherto used. I

"-It is wellknown that "chloroprene it2-chloroli3:=buta*diene) is "a valuable "and useful interme'diate. materiaF'for "the'productionof *a polymeric "material tresem-bling :natural rubber, but 'superior'tonaturalrubber'in somerespects. In particular, chloroprene 'po lymer "can be used in the "fabrication of articles for serviceconditions which are toolseverefor natural rubber. .For example, t;ch1oroprene withstands the action of petroleum solvents andfuels much moresuccess- Ifully"than does natural rubber. A principal method of preparing chloroprene has been by. the catalyzed; hydrochlorination of monovinyl acetylene, 'aprocess which .also resultsin' the concurrent? formation. of; appreciable quantities ofthe other aridless 'de'sirablechlorobutadiene isomers,.,and offdichlorobutenes. i The latter are formed byiithe furthera addition of hyjdrogenchloi'ide' to the: chlorobutadienes.,Another method bf. manufacturinglchloroprene .is '.;lcy'v the partial addition chlorination of butadiene "to 112dichlorobuteneT-3, and ,then subjecting .to dehydrochlorination '1; by "the ;action of a 'i'basic reagent. r IiThe :above and otherlmethods Wo f .i producing lchloroprene .all. require. affouncarbonatomtmolevc'illelin' the .coursecof, preparation. .Z'For; example, the .most common process'involves the v separate manufacture of monovinyl acetylene, which in turn requiredthe preparation. of ,a,pure v stream of'acetylene'by the calcium carbide process. ""The feed "materials for i'thei prior processes are. thus "relatively"expensive, orpas'in "the' caseofbutadiene; =much in dem-arid for other purposes, :par ticularly 'in times ofhational emergency. The objectCif-Q'ur invention isto' provide 'anew reaction for the manufacture or chloroprene. Another object is to provide a process Which-'does notazdependvuponaorirequire :a. supply-ref mono- -viny1 acetylene, butadiene orf other four-carbon atom materialiasaifeedz'stream. :Aifurther specifics-object is Y to LpIOVide :;-.a ;-process whereby .chloroprene can :be manufacturedain goodgyields Ldirectly. from-vinyllchloride. p l V cm its broadest terms, -.onneprocess.-.comprises the'heating of vinyl chloride to mild pyrolytic conditions, such thatasubstantial proportion of th'evinyl chloride,- pyrolizd is convertedto and is recoverable: as chloroprene. It has l..been "dis- "covered that *ch'loroprene,

although more 915- 2 .ceptible ,to thermal decomposition than vinyl ichlorideiitselfliis, nevertheless formed at the temperatures (required "for pyrolysis 'of tthe "vinyl chloride Tfee'd. material and is obtainedin good yield.

' i 'Ihe pyrolytic treatment is preferably carried outlinithe absence of ,any'catalyst or catalytic metal .iqsurfaces. The temperature of treatment is'inlthe jrangelof 450 C."tO"i65'O 0., the preferred vrange -of .operating .temperature being about 550'C. to 650 ..C. iThedesire'dreaction' is accomplished'by utilizing ashort contact time-.atfithe above; temperature, the fflowrof the vinyl chloride "feedbeing adjustedto, provide. a contact time ,in thelrangelo'f about Z-to 10. seconds. .Immediately on discharge iirom othe pyrolysis zone, the reacted streams is cooled .to .a temperature at which the chloroprene .Vcontent is relatively stable, the -chloroprene productibeing then recovered from ,the reacted mixture.

.The details of operation. of our process will-be morefullyzuriderstoodlfrom the following examples.

Example I A supply of' vinylzch'loride wasxvaporizedand ffedsatz-slightly tabove atmospheric pressureito ea reaction chamber consisting of i "a astainlessisteel "tixbe. T'Ihe tubeawas' fabricated of the 18 percent *chromium 8' 'percent nickel typealloy; designated as"type304bythe AmericanIron: and. Steel :Institute. The reactor itube was:;oneefourth inch: inside diameter' an'd; l2'zfeet long. :Thevinylxchloride 'vapoi wass fed-at" a:. rate providing a contact time'of 3:3 seconda'the tubelbeing maintainedqat a'temperature of 500 C;..by a'surrounding molten sait bath consisting of .a commerciallyzavailable eutectic 'mixtureof'sodiuminitrate and potassium nitrate. a 1

'Ihe product gases; leaving ."the reactor tube "were passed P through a 2 water cooled rheat- :exchanger to immediately reduceithe temperature below 100 C. and :stop iurtherrreaction; ;,Th,e cooled gases themwere passed :to' a: scoolingaand puiifidngsy'stem. 'Ihissystemi'included ai'cooler for cooling the gases to approximately lO-.C a water scrubber for absorption-"of rany :hydrogen chloride formdffollowe'd by a 'fdryen'for' removal tlf'vvater' vapor, and a final cooler operating at about -'"80 Ck to-cause condensation ofall liquefiable components. 'Nonecondensable components "such as acetylene or'. hydrogen "were" then vented toijthe atmosphere.

IExcessoLunreacted vinyl chloride was removed .from thegliqufied .product a by a i fractional "distillation. 'The bottoms cut of the'di'stillation was identified as chloroprene or 2-chloro-1,3-butadiene. The boiling range of the fraction at atmospheric pressure was 58-65 C. The density was 0.95 gram per cubic centimeter. The recognized corresponding properties of chloroprene are as follows: 59 C. boiling point, and 0.958 gram per cubic centimeter density.

Measurement of the amount of the chloroprene isolated and the quantity of hydrogen chloride absorbed showed that 78 percent of the vinyl chloride which was reacted was recovered as chloroprene. The degree of pyrolysis was kept at the low level of about 0.8 percent of the vinyl chloride fed, in order to insure the high yield obtained. Higher degrees of conversion or pyrolysis can, however, be obtained by the use of slightly higher reaction temperatures, as illustrated by the following example.

Example II Vinyl chloride was vaporized and subjected to thermal treatment by the same procedure as in Example I, except that the rate of feed was adjusted to provide a contact time of 4.2 seconds. In addition, the average temperature of the re-a action zone was raised to about 575 C. The amount of conversion was raised to 3.4 percent of the vinyl chloride fed. The yield of chloroprene was 66 percent of vinyl chloride reacted.

The product of our pyrolytic treatment has been further identified as chloroprene by means of forming an addition product with maleic anhydride, according to the method of Carothers (Journal American Chemical Society, volume 53, pages 4203-25 (1931)). Following that procedure, a portion of the material was reacted with an equal amount of fused maleic anhydride at atemperature above 50 C. The product of the reaction was crystallized from water solution and the melting point range determined to be l'71-171.4 C. The melting point of the corresponding derivative, made from a known chloroprene sample, is 171-172 C.

As will be seen from the foregoing examples, our process affords a convenient and straightforward method of producing chloroprene in good yields from vinyl chloride. As is well known, vinyl chloride is easily'manufactured by the addition of hydrogen chloride to acetylene, by the substitution chlorination of ethylene, or by the dehydrochlorination of ethylene chloride. process, therefore, allows rapid and efficient con-i version of ethane, ethylene, or acetylene, to chloroprene, by first converting to vinyl chloride by known methods and then manufacturing chloroprene according to the present process. The process is particularly advantageous in combination with an ethane chlorination plant. The chlorination of ethane is accompanied by the formation of appreciable amounts of 1,1-dichloroethane as well as other polychloroethanes. Although there is no particular demand for 1,1-dichloroethane, it is easily converted to vinyl chloride by dehydrochlorination, the vinyl chloride being then used according to the present process, for the manufacture of chloroprene.

In carrying out our process, it has been found particularly desirable to carry out the thermal treatment of the vinyl chloride in non-catalytic reactors, or at least, in reactor tubes of materials of very low catalytic activity.. It has been found that nickel or high nickel alloys should be avoided. In attempting to carry out the process in a pure nickel coil, plugging occurred very rapidly at temperatures of 500 C. or above owing to the Our 4 deposition of carbon in the tube. At temperatures at which no plugging occurred, there was no detectable conversion of the vinyl chloride feed.

The preferred materials of construction for the reactor tubes are the stainless or heat resisting steels of relatively low nickel content. Examples of such steels are those designated by the following type numbers by the American Iron and Steel Institute: 301, 302, 3023, 303, 304, 414, and 431. (Steel Products Manual, section 24, 1949). In addition to such heat resisting steels, the reaction can advantageously be carried out in nonmetallic tubes. For example, reactor tubes of vitreous silico are virtually entirely free of any catalytic activity, but of course suiier from the disadvantage of being fragile and expensive.

The specific diameter of the reactor tubes is not of, critical importance, providing they facilitate efficient heat transmission in the limited reaction time used. In general, we use reactor tubes with an internal diameter of less than two inches, and preferably of the order of one-half to one and one-half inches internal diameter.

As already described, the production of chloroprene by our process is made possible by the discovery that the pyrolysis of vinyl chloride is accompanied by the formation of chloroprene. Further, although the heat treatment of the vinyl chloride is necessarily carried out at a temperature at which the chloroprene is unstable, good recovery is nevertheless made possible by the restriction of the reaction period to a relatively brief period.

It has been found that the reaction time should be less than ten seconds, and preferably in the range of two to four seconds. At the lower reaction times, the reaction temperature is advantageously raised to obtain a reasonable conversion of the vinyl chloride feed. Thus, at contact periods of two to three seconds, temperatures of the order of 600 to 650 C. can advantageously be employed.

confining the reaction period or contact time of our process to restricted duration also means that provision is made, to terminate the reaction conditions promptly in the reactor outlet stream. Non-reactive conditions can be attained by several methods. The most convenient method involves the rapid cooling of the reactor outlet stream to a temperature of at least C. below the temperature of reaction. Another efficient method of providing stable conditions involves the dilution of the reactor outlet stream with an inert gas or a fresh supply of the vinyl chloride feed stream.

The preferred method of providing stable conditions is the rapid cooling above described, as it facilitates and is required for recovery of the chloroprene by flash condensation and subsequent distillation of the liquid phase produced.

Having fully described the manner of operating our process, what we desire to claim by Letters Patent is:

1. The method of preparing 2-chloro-'1,3-butad ene comprising pyrolytically treating vinyl chloride vapor at a temperature of 550 to 650 C. for a period of from two to ten seconds, then rapidly cooling the treated vapors to a temperature of at least 100 C. below the temperature of treatment and recovering the 2chloro-1,3-butadiene therefrom. V

2. The method of preparing 2-chloro-1,3-butadiene, comprising pyrolytically treatin g vin l chloride vapor ata temperature of about 450 to 650 C. for a period of from two to ten seconds, perature below 100 C., and recovering the 2-ch1othen rapidly cooling the treated vapors to a temro-1,3-butadiene therefrom. perature of at least 100 C. below the temperature JAMES H. DUNN. of treatment, and. recovering the 2-ch1oro-1,3- CLARENCE M. NEHER. butadiene therefrom. 5 PERCY W. TROTTER.

The methOd of Preparing z-chloro-lfi-buta- References Cited in the file of this patent diene, comprising pyrolytically treating vinyl chloride vapor at a temperature of about 500 C. UNITED STATES PATENTS for a period of from about two to four seconds, Number Name Date then rapidly cooling the treated vapors to a tem- 10 2,379,708 Hearne July 3, 1945 

2. THE METHOD OF PREPARING 1-CHLORO-1,3-BUTADIENE, COMPRISING PYROLYTICALLY TREATING VINYL CHLORIDE VAPOR AT A TEMPERATURE OF ABOUT 450* TO 650*C. FOR A PERIOD OF FROM TWO TO TEN SECONDS, THEN RAPIDLY COOLING THE TREATED VAPORS TO A TEMPERATURE OF AT LEAST 100*C. BELOW THE TEMPERATURE OF TREATMENT, AND RECOVERING THE 2-CHLORO-1,3BUTADIENE THEREFROM. 